This invention relates to a supersonic diffuser with a non-axisymmetric design.
The design of supersonic diffusers, as used in supersonic wind tunnels is well understood. The flow mechanism primarily relied upon is the pseudo shock, which requires a duct length on the order of 10 duct diameters, to produce pressure recovery close to that of a normal supersonic shock. Blade systems have been used in prior art diffusers so that the length of the diffuser channel can be shortened. See the article "High-Efficiency Supersonic Diffusers" by Neumann and Lustwerk, pages 369-374, Journal of the Aeronautical Science, June 1951. Wind tunnel diffusers are normally close to an axisymmetrical design, that is, either round or square.
In diffuser channels which are not axisymmetrical, such as channels with a rectangular cross section of large side ratio, the pseudo-shock system suffers greatly with only about 65% of the normal shock recovery obtained.
Any diffuser channel, which is not axisymmetrical can be provided with a blade system which will divide the channel into ducts with approximately square cross sections which are substantially symmetrical around their own axis. Thus, while the blade systems were used in prior art devices only for the purpose of permitting the use of shorter channel length, they will also inherently perform the function of increasing the pressure recovery, when used in non-axisymmetrical channels. Though these blade systems increase wall friction, these losses are insignificant in comparison to the losses in the diffuser channel when they are not used.
In a diffuser channel wherein an internal blade system is used with a device having at least one wall extending forward of the diffuser channel, wherein the flow is directed into the diffuser channel with a certain flow distribution and with a boundary layer formed on the wall ahead of the diffuser channel, the diffuser duct, adjacent said one wall, are burdered by the boundary layer which is formed on the wall ahead of the diffuser and ingested into these ducts. It has been found that this greatly affects the pressure recovery of the diffuser.